The present invention relates to so-called release systems (declutching devices) for friction clutches, and more particularly to improvements in self-adjusting release systems for the friction clutches of motor vehicles or the like. Still more particularly, the invention relates to preferably self-adjusting release systems for friction clutches of the type wherein an antifriction bearing or analogous clutch-actuating component is movable into deforming or displacing engagement with a clutch portion (such as the prongs of a diaphragm spring) which thereupon causes disengagement of the clutch, i.e., cessation of transmission of torque from a rotary input element (such as the flywheel or crankshaft of an internal combustion engine) to a rotary output element (such as the input shaft of a change-speed transmission in a motor vehicle).
It is already known to provide in a clutch release system a pair of levers which are pivotably mounted in the bell-shaped housing of the friction clutch. One of the levers is used to pivot the other lever and the other lever can be pivoted to a position in which it urges the bearing against the diaphragm spring to thereby disengage the clutch. When not pivoted, the one lever is caused to abut against a stop while the clutch is engaged, i.e., while the other lever ceases to urge the bearing against the diaphragm spring. The angular positions of the two levers relative to one another are adjustable in order to compensate for wear upon the friction linings of the clutch. The one lever is pivotable by the clutch pedal and the two levers are connected to each other by a coupling device which is effective only when the one lever is pivoted by the pedal in a (first) direction in order to pivot the other lever toward engagement with the bearing and to thereby shift the bearing into engagement with the diaphragm spring of the clutch.
Release systems of the above outlined character are often employed in motor vehicles in order to compensate for wear upon the friction linings and/or pressure plates of the clutch which serves to transmit torque from the output element of the engine to the input element of the change-speed transmission. The self-adjusting feature of the release system is desirable and advantageous because it ensures that the extent of depression of the clutch pedal preparatory to shifting into a different gear will remain at least substantially unchanged in spite of the aforementioned wear upon one or more parts of the friction clutch. The wear can be especially pronounced upon the prongs of the diaphragm spring, upon the friction linings of the clutch disc, upon the pressure plates which flank the clutch disc, upon the linkage which transmits motion from the clutch pedal to the one lever of the release system, upon the coupling between the two levers and/or upon any other part or parts which, as a result of extensive wear, could induce a change in the extent of depression of the clutch pedal for the purpose of disengaging the clutch. As mentioned above, one presently popular automatic self-adjusting feature includes the provision of means for allowing or causing automatic changes in the mutual angular positions of the two levers in response to progressing wear upon one or more of the aforeenumerated parts. As a rule, the lever which can engage the bearing is mounted for angular movement relative to the lever which is pivoted by the clutch pedal, and such automatic angular adjustment takes place when the clutch is engaged, i.e., when the operator of the vehicle does not maintain the clutch pedal in depressed position. This ensures that, when the clutch pedal is depressed, the extent of its movement to depressed position is not affected by the wear upon one or more parts of the clutch and/or of the release system because the lever which acts upon the bearing has changed its position relative to the lever which is operatively connected with the clutch pedal.
Many motor vehicles, especially heavy-duty motor vehicles which are used for hauling of heavy loads and/or vehicles which are used at construction sites, must be equipped with brakes for the input elements of their change-speed transmissions. Such brakes are or must be provided in addition to the aforediscussed self-adjusting release systems. Immediate braking of the input shaft of the changespeed transmission in response to disengagement of the clutch (i.e., in response to cessation of torque transmission from the engine to the transmission) is desirable and advantageous because it ensures more rapid, more predictable and more reliable shifting into a different gear. In accordance with a presently known proposal, the brake is actuated by the antifriction bearing which is movable by the other lever of the release system in order to deform or displace the diaphragm spring of the friction clutch. The brake then decelerates or arrests the input shaft of the change-speed transmission not earlier than on disengagement of the clutch. A presently used device for actuating the brake comprises two coaxial sleeves and an axially acting adjusting device (such as a freewheel employing clamping elements) or an angularly acting adjusting device therebetween. One of the sleeves serves to act upon a mobile clutch component (such as upon the radial prongs of the diaphragm spring) and the other sleeve receives motion from the clutch pedal to displace the one sleeve as well as to actuate the brake for the input shaft of the change-speed transmission. In such release systems, the adjusting means between the two sleeves compensates for wear to thereby ensure that the extent of depression of the clutch pedal remains unchanged as well as to ensure that the brake for the input shaft of the transmission is actuated irrespective of eventual wear upon the parts which are disposed between the other sleeve and the pedal.
The just discussed brake actuating system exhibits a number of serious drawbacks. Thus, it is very complex, sensitive, prone to malfunction and expensive. Moreover, it takes up a substantial amount of space which is always at a premium under the hood of a motor vehicle. Still further, it comprises a large number of discrete parts which contributes to initial cost, to the cost of assembly as well as to maintenance cost.